This invention is directed to silicone copolymers prepared by nonaqueous interfacial polymerization, where polycondensation takes place at the interface between reactive starting materials dissolved in separate and immiscible solvents.
A major advantage of interfacial polymerization of silicon containing monomers is the ability to control the structure of the resulting polymer chain and the composition of the copolymer, without the need for a conventional catalyst, and without problems associated with rearrangement during polymerization.
Interfacial polymerization of certain organic monomers is a known polycondensation reaction wherein monomers are dissolved in immiscible solvents. Polymerization occurs when the monomer in one phase diffuses from the bulk of the solution into the interface, and reacts with the monomer from the other phase. The polymerization rate depends on the diffusion rate and reactivity of the functional groups on the monomers.
With respect to our invention, a nonaqueous interfacial polymerization can be conducted using a dihalopolysiloxane (preferably a dichloropolysiloxane) dissolved in one phase, and a potassium silanolate or other metal silanolate dissolved in the other phase. High molecular weight polysiloxanes and potassium chloride or other chloride salt are formed at the interface.
Since the inorganic salt by-product is not soluble in the organic solvent phases, it precipitates and does not interfere with the polycondensation. If the copolymer is insoluble in either solvent phase, it also precipitates and can be removed from the interface.
Among conventional interfacial polymerization reactions are the polycondensation of amines with acetyl chloride to form nylon (i.e., polyamides), and the reaction of alcohols with acids to form polyesters. Interfacial polymerization of these organic monomers typically provides faster polymerization rates than other types of polymerization reactions such as bulk or solution polymerization. Even more important is the fact that because stoichiometry between the monomers need not be precise, a higher molecular weight polymer can be obtained.
This is particularly critical for organic polycondensation reactions where an imbalance of a fraction of a percent causes the extent of polymerization to be greatly affected. Another advantage of interfacial polymerization is the formation of high molecular weight polymers at the interface, regardless of the overall percent conversion of the bulk amounts of the two monomeric reactants still in solution.
Among other of the advantages offered by interfacial polymerization reactions in the synthesis of organic polymers are (i) the ability to prepare infusible polymers; (ii) the ability to synthesize polymers with chemically active substituents as well as heteroatoms; (iii) controlled crosslinking of the polymer structure; (iv) the ability to use cis- and trans- conformation without rearrangement; (v) the ability to prepare optically active polymers without decomposition of the intermediates; (vi) the ability to use short-chain and ortho-substituted ring intermediates; (vii) the ability to use thermally unstable intermediates to form thermally stable polymers; (viii) the ability to form block and ordered copolymers; (ix) the ability to form synthetic elastomers; (x) a direct method of forming polymer solutions and dispersions; (xi) a direct method for the polymerization and formation of polymer coatings and encapsulants; and (xii) a direct method for polymerization of monomers into fibrous particulates, fibers, and films.
We have discovered that many of these advantages can be directly correlated and applied to the interfacial polymerization of silicon containing monomers in forming siloxane copolymers.